Significant reduction of colony number, bacterial area coverage, colony size, and bacterial migration were demonstrated on Sharklet surfaces compared with smooth control surfaces regardless of time point, type of growth media, or Sharklet pattern type (). The SEM bacterial area coverage analysis offered a more consistent measurement method for evaluating bacterial load on sample surfaces compared with the colony enumeration method. Although a similar result in degree of reduction of bacterial load was obtained for the colony enumeration method, the variances were larger. The incalculable variability between results of the viable plate count technique has been well documented and is likely because of the inconsistency in disaggregating biofilm.14
Biofilm harvesting and disaggregation remain imprecise and biased techniques, despite the use of sonication and vortex mixing methods for removal of surface-attached populations.15,16
This remains a critical area of research as debate among biofilm experts continues.14,17
Imaging of biofilms avoids many of the limitations of colony dispersal and enumeration.17
The unique nature of the Sharklet technology, which has no active kill mechanism and includes no biocidal agents, needs new techniques to quantify the antimicrobial effect.
FIG. 7. Compiled percent reductions for all measurement parameters comparing Sharklet surfaces with smooth. Chart represents compiled data for all Sharklet surface types at various time points for both artificial urine and tryptic soy broth. Data are compiled (more ...)
The reduction in colony size on the Sharklet surfaces could be an indicator for the inhibition of colony proliferation. The exact mechanism of the Sharklet inhibitory effect on bacterial colonization and proliferation continues to be explored.18,19
Biofilm communities generally exist as large groups of attached cells, forming an exopolysaccharide matrix to house the community,20
which are not observed on the Sharklet micropatterns. It is reasonable that limiting bacterial colony size would inhibit biofilm expression. This observed biofilm phenomenon is important because of its relevance to the pathogenesis of device-related infections and needs further investigation.
Interestingly, the Sharklet micropatterns also effectively inhibit bacterial migration compared with smooth surfaces. This effect has important implications for preventing CAUTI, because the mode of bacterial access into the bladder is primarily via extralumenal migration of bacteria that originate from the interface between the urethral meatus and catheter external surface.3
An important result from this experiment was the indication that the transverse Sharklet feature orientation offered a more significant reduction in migration than the parallel orientation. This behavior may be related to the physical barrier created by the features of the Sharklet micropattern when oriented perpendicular to the overall direction of migration. It is worth noting that this species of E coli
did not have any swimming or swarming motility and, thus, no apparent mechanistic drive for migration, possibly explaining the low incidence of migration for even the smooth control rods. Future migration studies will be conducted using motile species of other uropathogens in an in vitro
migration model that more closely resembles the in vivo
The Sharklet micropattern represents a paradigm shift in the current strategy using chemical modifications to surfaces of medical devices, instead relying on a microscopic texture to provide an inhospitable surface for microorganism colonization. Existing Foley catheters aimed at inhibiting bacterial colonization of the catheter surface all rely on antimicrobial agents incorporated into the catheter material or applied onto the catheter surface. These formulations have not been shown to produce statistically significant reductions in the incidence of symptomatic CAUTI. Although some antimicrobial-based formulations have been associated with reduction in bacteriuria, the use of certain agents could eventually lead to emergence of antimicrobial resistance in the presence of exceedingly high bacterial counts in the catheterized bladder. The unique micropatterning approach of the Sharklet design offers an antimicrobial function that does not rely on antimicrobial agents.
While previous studies have examined the use of microscopic surface structures to direct microorganism attachment,23,24
the Sharklet pattern is the first microscopic surface texture designed to inhibit bacterial colonization and migration. Explanation of the mechanism behind this unique effect to prevent microorganism colonization through microscopic texture alone has led to an “Engineered Roughness Index” and other models of material properties that affect microorganism behavior.18,25,26